The present invention relates to methods and devices used to measure and record physiological data, such as blood pressure and electrocardiogram data. More particularly, the invention relates to a method and a system of distinguishing components of physiological activity waveforms.
Modern medical practice involves monitoring a variety of physiological data, including electrical activity and blood pressure. Electrocardiograms (ECG) are used to measure electrical activity that controls the contraction of the heart. As is known, prominent parts of an ECG are the P wave, a deflection caused by the current originating in the atrium; the QRS complex, which represents the electrical activity of the ventricles as they contract; and the T wave, which denotes ventricular relaxation. These changes in electrical activity may, in general, be sensed using electrodes attached to the body.
The pulsatile pressure of blood in the circulation system may be measured in a variety of ways and provides different information depending on where the pressure is measured. For example, central venous pressure (CVP) or right atrial pressure (RAP) measurement provides useful information about cardiovascular status and right ventricular function. Frequently, CVP and RAP measurements are used to monitor the volemic state and right heart function.
xe2x80x9cPulmonary artery pressure monitoring provides additional information about heart function. One measurement that may be made with a pulmonary artery catheter is the pulmonary artery wedge pressure (PAWP). In this measurement, a balloon near the end of the catheter is inflated, occluding flow through that branch of the pulmonary circulation (as shown in FIG. 1). When so positioned, the balloon is said to be wedged in the pulmonary artery. The stagnant blood at the distal tip of the catheter is, in effect, at the same pressure as the blood in the left atrium, which, when the mitral valve is open, is also at the same pressure as the blood in the left ventricle. During the PAWP measurement, the pulmonary artery waveform takes on a dampened appearance, because the pressure waveform represents the left atrial pressure rather than the pulsatile pulmonary artery pressure. Prominent parts of the PAWP waveform may be identified and correlated to the subject""s ECG. An xe2x80x9caxe2x80x9d wave is produced by left atrial contraction and follows the P wave of the ECG. The descending portion of the xe2x80x9caxe2x80x9d wave is called the x-descent, reflecting left atrial relaxation. A small positive deflection is sometimes visible on the x-descent. This deflection, called the xe2x80x9ccxe2x80x9d wave, is produced by the closure of the mitral valve. The xe2x80x9cvxe2x80x9d wave is produced by the filling of the left atrium against the closed mitral valve during ventricular systole and, therefore, occurs after the R wave of the ECG (more precisely, it occurs after the T wave of the ECG). The downstroke following the peak of the xe2x80x9cvxe2x80x9d wave is termed the y-descent, which represents the opening of the mitral valve and a decrease in left atrial pressure and volume during passive emptying into the left ventricle.xe2x80x9d
Because the PA catheter is in effect sensing the pressure of the left atrium during the wedge pressure measurement, the PAWP provides the same information about left heart function as RAP measurements provide about right heart function. Thus, the morphology of the RAP and PAWP waveforms is similar, the only difference being in origin: the components of the RAP waveform are due to right heart activity, while the PAWP components are due to left heart activity. Like a PAWP waveform, a RAP waveform also has xe2x80x9caxe2x80x9d, xe2x80x9ccxe2x80x9d, and xe2x80x9cvxe2x80x9d waves. FIG. 2 illustrates exemplary ECG, RAP, and PAWP waveforms.
xe2x80x9cBecause of the time required for the mechanical event to reach the sensing device, the xe2x80x9caxe2x80x9d wave in a RAP waveform is generally observed about 80-100 msec after the P wave in an ECG. The xe2x80x9caxe2x80x9d wave in a PAWP waveform is generally observed about 200-240 msec after the P wave. As noted, the decline in pressure that immediately follows the xe2x80x9caxe2x80x9d wave is termed the x-descent and reflects atrial relaxation (right atrium for RAP, left for PAWP). The xe2x80x9ccxe2x80x9d wave is a minor wave that may appear as a distinct wave or as a notch on the xe2x80x9caxe2x80x9d wave, or may be absent altogether. It reflects a slight increase in pressure in the atrium produced by closure of the valve (tricuspid valve for RAP, mitral valve for PAWP). The time difference between the xe2x80x9caxe2x80x9d and xe2x80x9ccxe2x80x9d waves approximates the PR interval of the ECG waveform. The xe2x80x9cvxe2x80x9d wave is generally observed near the end of the T wave of the ECG waveform in the RAP waveform or during the TP interval in the PAWP waveform. The y-descent is produced by the opening of the valve (tricuspid valve for RAP, mitral valve for PAWP).xe2x80x9d
xe2x80x9cNormal mean pressure values are 2-6 mmHg for RAP and 4-12 mmHg for PAWP. Under normal (nonpathologic) conditions, the xe2x80x9caxe2x80x9d and xe2x80x9cvxe2x80x9d waves are small and of approximately equal amplitude. Instances in which either the xe2x80x9caxe2x80x9d or xe2x80x9cvxe2x80x9d wave is elevated more than 2 or 3 mmHg above the other wave are indicative of valvular pathologies or ventricular failure. Although it is known that detecting and measuring xe2x80x9caxe2x80x9d, xe2x80x9ccxe2x80x9d, and xe2x80x9cvxe2x80x9d waves provides useful information like that just noted, detecting and measuring these waveform components is not an easy task, particularly when reviewing waveforms on a monitor screen. In fact, the usual practice is to print a strip recording of pressure and simultaneous ECG waveforms and, using a straight edge, line up the electrical events with the mechanical (pressure) events. Complicating things further, there are circumstances caused by a patient""s medical condition where it is difficult to differentiate large xe2x80x9cvxe2x80x9d waves from regular pulmonary artery pressure pulses on the pressure tracing.xe2x80x9d
Accordingly, there is a need for an improved method and system that identifies components of pressure waveforms. In particular, there is a need for a method and system that assists clinicians in identifying pressure waveform components on a monitor screen.
In one embodiment, the invention provides a system that identifies components of a waveform. The system includes an ECG acquisition module, a pressure waveform acquisition module to acquire a pressure waveform, and an analysis module coupled to the ECG acquisition module and the pressure waveform acquisition module. A monitor or similar display device is coupled to the analysis module.
The analysis module establishes a time reference based on R waves in an ECG, determines a first interval in the pressure waveform between a first point offset a predetermined amount ahead of a first R wave and a second point offset a predetermined amount behind the first R wave. The analysis module also identifies the highest peak of the pressure waveform in the first interval, identifies a second R wave in the ECG subsequent in time to the first R wave, establishes a second interval that extends from the second point to a third point, where the third point is positioned at a distance ahead of the second point equal to a first percentage of the interval from the second point to a predetermined amount behind the second R wave. The analysis module also identifies the highest peak in the pressure waveform in the second interval, establishes a third interval that extends from the highest peak in the first interval to a fourth point positioned at a distance ahead of the highest peak in the first interval equal to a second percentage of the distance between the highest peak in the first interval and the highest peak in the second interval, and identifies the highest peak in the pressure waveform in the third interval.
After identifying the peaks, the analysis module generates an output signal that causes a monitor to display a waveform representing the pressure waveform such that the identified highest peaks of the pressure waveform in the first, second, and third intervals are distinguished from each other and the rest of the displayed waveform.
In another embodiment the invention provides a method of identifying waves in a pressure waveform. The method includes displaying the waveform; establishing a time reference based on R waves in an ECG; determining a first interval in the pressure waveform between a first point offset a predetermined amount ahead of a first R wave and a second point offset a predetermined amount behind the first R wave; and identifying the highest peak of the pressure waveform in the first interval.
Once the highest peak of the pressure waveform in the first interval is identified, a second R wave in the ECG subsequent in time to the first R wave is identified. Following the identification of the second R wave, the method involves establishing a second interval that extends from the second point to a third point, the third point being positioned at a distance ahead of the second point equal to a first percentage of the interval from the second point to a predetermined amount behind the second R wave. The highest peak in the pressure waveform in the second interval is identified. Then a third interval is determined. The third interval extends from the highest peak in the first interval to a fourth point positioned at a distance ahead of the highest peak in the first interval equal to a second percentage of the distance between the highest peak in the first interval and the highest peak in the second interval. The method also includes identifying the highest peak in the pressure waveform in the third interval and modifying the displayed waveform such that the identified highest peaks of the pressure waveform in the first, second, and third intervals are distinguished from each other and the rest of the pressure waveform. It is preferable that the peaks be distinguished according to a color scheme.
As is apparent from the above, it is an advantage of the invention to provide a method and system of identifying pressure waveform components. Other features and advantages of the invention will become apparent by consideration of the detailed description and accompanying drawings.